In recent years, it has been practiced to perform communication between many apparatuses by using Internet Protocol (IP). Also, “Mobility Support in IPv6 (MIPv6)” has been developed by the Internet Engineering Task Force (IETF) to provide mobility support for the mobile apparatuses (See the Non-Patent Document 1 given below). In MIPv6, each mobile node has permanent home domain. When a mobile node is connected to a home network, a primary global address called “home address” (HoA) is assigned. When a mobile node is away from the home network, i.e. when it is connected to other external network, a temporary global address known as “care of address” (CoA) is assigned. In the concept of the mobility support, even when a mobile node is connected to other external network, a packet addressed to the mobile node can reach its home address. This is accomplished when an entity known as a home agent (HA) is introduced in the home network as described in the Non-Patent Document 1.
A mobile node registers its care of address by using a message, which is known as Binding Update (BU) message, to a home agent. As a result, the home agent can generate the association to associate the home address of the mobile node with the care of address. The home agent intercepts the message of the mobile node to the home address and has responsibility to transfer the packet to the care of address of the mobile node by encapsulating the packet (this is known as packet tunneling) (i.e. to place the packet on a payload of a new packet).
With the propagation and the increase of wireless apparatuses, it can be predicted that new classes of mobility technique would appear. Among such techniques, total network of the node changes the points of connection in the network mobility (NEMO). If the concept of the mobility support for individual hosts is extended to the mobility support of the network of nodes, the objective is to offer a mechanism, such that the node in the mobile network can be located and connected to any segment in the Internet and can be reached by primary global address.
As disclosed in the Non-Patent Document 2 and the Patent Document 1 as given below, IETF has developed a solution for network mobility. In these documents, it is described that network prefix used by the node in mobile network is given within BU when a mobile router (MR) transmits BU to a home agent. Also, it is described that it is inserted into BU by using a specific option known as Network Prefix Option. In doing so, the home agent builds up a routing table based on prefix, and it is possible to transfer the packet transmitted to the destination having these prefixes based on the table to the care of address of the mobile router.
In the Non-Patent Document 1, discussion is made on global mobility support for the mobile node, and a full route optimization (RO) is disclosed, which uses the procedure of return routability (RR) between a mobile node and a correspondent node (CN). In the Non-Patent Document 2, discussion is made on network mobility support, which gives no specific consideration on route optimization. In both of these documents, no serious consideration is given on home network model for the mobile node. In normal assumption, a home agent is a fixed router in a home sub-network. Even when the home agent may be mobile, the techniques described in the Non-Patent Documents 1 and 2 can merely support peer-to-peer packet transmission. However, there are some inconveniences as to be described below.
There are several methods to build up home network for mobile node including the arrangement of mobile home network. As a conceivable example of such arrangement, there is a case where the home network, to which the mobile node is connected, is movable, and the mobile router of this mobile home network has its own fixed home agent (known as root HA). The model of such home network model is possible in case the home agent of the mobile node is also a mobile router or in case the home agent of the mobile node is connected to a mobile network behind the mobile router.
Description will be given on one example where such case occurs. A root HA can be arranged at “corporate headquarters”. A mobile home network, which uses this root HA as a default router can be assigned to “Sales Dept.”, which moves from a local office to another local office. Also, the mobile node using the root HA connected to this mobile home network is maintained by the staffs of the Sales Dept. As another example of arrangement, the case of fire department or police station can be conceived. In this case, the root HA may be assigned to “Regional Headquarters”. This mobile HA is maintained by a mobile patrol car, for instance, and the mobile node using this mobile home network is maintained by fire department staffs or by policemen.
Quasi-optimization of the route occurs when MIPv6 and NEMO basic supports become effective regardless of whether the mobile HA is positioned together with the mobile router or it is positioned behind the mobile router. Description will be given below. FIG. 13 gives an example of problem, in which quasi-optimization of route occurs when the position of HA is changed. In this arrangement example, a mobile node (MN) 130 currently connected to an external access router (AR) 148 has a home network (mobile network) 104 and the mobile network 104 is also moved from the initial position (home network 102). HA 114 in the home network 104 is a home agent of MN 130, and it is connected to MR 124, which is a default router. The home network of MR 124 is a home network 102. The root HA, i.e. the home agent of MR 124, is HA 112 in the home network 102. In the arrangement example, the home network 102 of MR 124 is fixed. When MN 130 and CN 150 want to perform data communication, the data communication between these peer nodes would be carried out via a global communication network 100 (e.g. Internet).
FIG. 14 shows data communication path between MN 130 and CN 150 when MIPv6 and NEMO basic supports are used at the mobile node and the mobile router. If it is assumed that route optimization cannot be achieved by MN 130 and CN 150, the data path will be as given below. MN 130 tunnelizes a data packet addressed to HA 114. In this case, MR 124 is away from home, and HA 112 would have prefix of mobile network 104 in the binding cache entry (BCE). Therefore, the tunnelized data packet to be sent to HA 114 passes through a path 160 and is intercepted by HA 112. The reason is that HA 112 discovers the concurrence of the longest prefix as the address of HA 114 in BCE. HA 112 further encapsulates this packet and tunnelizes it via a path 162 to transmit it to MR 124.
When this packet is received, MR 124 decapsulates it and delivers the inner packet to HA 114. HA 114 further decapsulates this packet and tries to transfer it to its destination CN 150. This data packet passes through MR 124, which is a default router. Using NEMO basic support, MR 124 tunnelizes this packet via a path 163 and sends it to HA 112. When this packet is received, HA 112 decapsulates it and transfers the packet inside, which is destined to CN 150, via a path 164 to CN 150.
Therefore, when basic standardized protocols are used by the mobility pattern, it is evident that the data path between the mobile node and CN makes a long detour. Even when route optimization can be achieved between two peer entities, RR (Return Routability) relating to signaling using the home agent is to be turned to an inefficient path by the moving.
The Non-Patent Document 3 describes a method to transfer from a home agent to another home agent for the purpose of load balancing in MIPv6. This method is primarily processed at the home agent. That is, the load between a plurality of home agents is balanced on home link according to the number of packets to be tunnelized. This equilibration or balancing of the load is achieved by a plurality of server home agents having replicated data rather than the partitioned server home agent. The method of the partitioned server home agent is used in normal MIPv6. Here, the home link of the mobile node has a multiple of home agents, and the mobile node selects one home agent according to the number of the advertised and desirable home agents. The home agent can realize static load balancing by changing the desirable level when transmitting a router advertisement (RA) message.
In the method based on duplication, the mobile node selects the home agent at random when it wants to start registration, but the home agent under the control is not fixed during the period when registration remains effective. When the new registration is received, the home agent sends binding information to all home agents in the home link. After a certain time has elapsed or after several packets of threshold value, the control is given to another adequate home agent. The new home agent controls the packet addressed to the mobile node in BCE and acts as a proxy for a mobile host. According to this method, therefore, the purpose when BCE is shifted from the home agent to another home agent is basically for load balancing. Also, the mobile host recognizes this shifting of BCE.
The Non-Patent Document 4 given below proposes a protocol to perform balancing of the load between the home agents in the home link and to switch over to a new home agent by detecting failure of the home agent. This protocol does not depend on RA to prepare a list of home agents but uses hello message in the home link for the preparation of the list of home agents. Each mobile node or each mobile router carries out Dynamic Home Agent Discovery (DHAAD) and discovers an adequate home agent. This home agent is called “primary home agent”. After the mobile node registers the binding to this primary home agent, the primary home agent sends the binding cache entry to another home agent in the home link. This is used for the purpose of balancing the load so that any home agent of the home link can send a proxy message for prefix of mobile node and the data packet can be tunnelized to the current care of address of the mobile node.
In addition, when failure occurs in the primary home agent, or for the purpose of balancing the load, the switching of the primary home agent is carried out by a backup node. At the time of failure, the backup node sends a request for switching, or the primary home agent sends a request for switching to the mobile node for load balancing. This method is used for the load balancing and for the discovery of the failure and it is not for route optimization by the mobile home agent.
In the Non-Patent Document 5, distributed (decentralized) home network model is used for three purposes, i.e. redundancy of the home agent, load sharing between the home agents, and route optimization. This method is particularly useful for route optimization of NEMO. According to this method, one primary home agent is selected from the distributed home network. The distributed home agents have the same anycast address. By the anycast message, the closest home agent is selected as the primary home agent.
In this protocol also, a home agent BCE delegation mechanism similar to the one described in the Non-Patent Document 4 is used. According to this method, the mobile router can obtain a new home agent in the neighborhood by executing DHAAD when it is moved to a new link, and it is particularly useful for solving the problem of a moving home agent. However, the problem lies in that this solution is for the distributed home network mode. On the other hand, the solution according to the present invention is not for the distributed home network model. In this case, there are a multiple of signalings such as hello message between home agents or binding synchronization message. Further, when the home agent in the home domain moves, the correspondent closer to the home domain cannot send the data to the mobile node by finding an adequate home agent in the home domain. Therefore, it is better that the home agent in the home domain has always BCE of the mobile node. Also, according to this method, when the home agent moves, BCE of all home agents belonging to the distributed home network must be updated, and this makes the matter very complicated. Accordingly, if possible, it is better to find a home agent, which is in rest position.
In the Non-Patent Document 6, discussion is made on a method similar to that of the Non-Patent Document 5 except the following point: In the Non-Patent Document 6, a proxy MIP is introduced for local mobility management and for route optimization. In addition, distributed home network model is used. In the distributed home network, the home agents exchange BCE with each other when they are away from the home network, and all home agents belonging to different home network models maintain the tunnel between the home agents. The tunnel can be maintained by a certain routing protocol. This method is a method to reinforce the Non-Patent Document 5, and route optimization can be accomplished during the MR-to-MR communication.
According to the Patent Document 2, delegation of BCE from home agent to home agent is given for the reason of load balancing, and there are one primary home agent and several secondary home agents. When the load on the primary home agent is increased, the primary agent delegates transmission right to the secondary home agent in transmissive (transparent) manner so that the mobile node does not become aware of it. However, the primary home agent is still controlling the mobile node, and all binding messages are transmitted and processed by the primary home agent. The secondary home agent merely acts as a proxy for the mobile node or for the mobile router and intercepts the packet addressed to the mobile node. Further, when a packet to be sent to the mobile network node (MNN) attached to a MR, or a mobile node, is tunnelized, the secondary home agent uses the address of the primary home agent as source address of the tunnel.    [Patent Document 1] Leung, K. K., “Mobile IP mobile router”, U.S. Pat. No. 6,636,498, October 2003.    [Patent Document 2] Haverinen, Henry, “Load balancing in telecommunications system supporting mobile IP”, EP 1 134991 B1, 23 Jun. 2004.    [Non-Patent Document 1] Johnson, D. B., Perkins, C. E., and Arkko, J., “Mobility Support in IPv6”, Internet Engineering Task Force (IETF) Request For Comments (RFC) 3775, June 2004.    [Non-Patent Document 2] Devarapalli, V., et. al., “NEMO Basic Support Protocol”, Internet Engineering Task Force (IETF) Request For Comments (RFC) 3963, January 2005.    [Non-Patent Document 3] Jason P. Jue and Dipak Ghosal, “Design and Analysis of replicated Servers to Support IP-Host Mobility in Enterprise Networks”, Communications, 1997, pgs 1256-1260.    [Non-Patent Document 4] Devarapalli, V., Wakikawa, R., and Thubert, P., “Local HA to HA protocol”, IETF Internet Draft: draft-devarapalli-mip6-nemo-local-haha-00.txt, Work-In-Progress, Jan. 2, 2006.    [Non-Patent Document 5] Wakikawa, R., Devarapalli, V., and Thubert, P., “Inter Home Agents Protocol (HAHA)”, IETF Internet Draft: draft-wakikawa-mip6-nemo-haha-01.txt, 16 Feb. 2004.    [Non-Patent Document 6] Thubert, P., Wakikawa, R., and Devarapalli, V., “Global HA to HA protocol”, IETF Internet Draft: draft-thubert-nemo-global-haha-01.txt, expires Apr. 18, 2006.
When discussion is made on the prior art as given above, it is apparent that many solutions have been proposed for load balancing under home link or distributed home link environment. However, none of the prior art gives consideration on the state where home agent moves, i.e. the state where the home agent is positioned in mobile network. Accordingly, problems of inefficient routing may occur for the mobile node in the mobility as described above.